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A371786
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a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(4*n-k,n-2*k).
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2
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1, 4, 27, 209, 1716, 14553, 125971, 1105885, 9809019, 87691592, 788832045, 7131655908, 64743390321, 589808771881, 5389066722654, 49365637128655, 453212161425716, 4168951499299185, 38415242186255419, 354527945536409116, 3276414018301664025
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = [x^n] 1/((1-x+x^2) * (1-x)^(3*n)).
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PROG
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(PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(4*n-k, n-2*k));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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